package org.apache.lucene.analysis;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.Set;

/**
 * Removes stop words from a token stream.
 */

public final class StopFilter extends TokenFilter {

    private final Set stopWords;
    private final boolean ignoreCase;

    /**
     * Construct a token stream filtering the given input.
     */
    public StopFilter(TokenStream input, String[] stopWords) {
        this(input, stopWords, false);
    }

    /**
     * Constructs a filter which removes words from the input
     * TokenStream that are named in the array of words.
     */
    public StopFilter(TokenStream in, String[] stopWords, boolean ignoreCase) {
        super(in);
        this.ignoreCase = ignoreCase;
        this.stopWords = makeStopSet(stopWords, ignoreCase);
    }

    /**
     * Constructs a filter which removes words from the input
     * TokenStream that are named in the Hashtable.
     *
     * @deprecated Use {@link #StopFilter(TokenStream, Set)} instead
     */
    public StopFilter(TokenStream in, Hashtable stopTable) {
        this(in, stopTable, false);
    }

    /**
     * Constructs a filter which removes words from the input
     * TokenStream that are named in the Hashtable.
     * If ignoreCase is true, all keys in the stopTable should already
     * be lowercased.
     * @deprecated Use {@link #StopFilter(TokenStream, Set)} instead
     */
    public StopFilter(TokenStream in, Hashtable stopTable, boolean ignoreCase) {
        this(in, stopTable.keySet(), ignoreCase);
    }

    /**
     * Construct a token stream filtering the given input.
     * @param input
     * @param stopWords The set of Stop Words, as Strings.  If ignoreCase is true, all strings should be lower cased
     * @param ignoreCase -Ignore case when stopping.  The stopWords set must be setup to contain only lower case words 
     */
    public StopFilter(TokenStream input, Set stopWords, boolean ignoreCase) {
        super(input);
        this.ignoreCase = ignoreCase;
        this.stopWords = stopWords;
    }

    /**
     * Constructs a filter which removes words from the input
     * TokenStream that are named in the Set.
     * It is crucial that an efficient Set implementation is used
     * for maximum performance.
     *
     * @see #makeStopSet(java.lang.String[])
     */
    public StopFilter(TokenStream in, Set stopWords) {
        this(in, stopWords, false);
    }

    /**
     * Builds a Hashtable from an array of stop words,
     * appropriate for passing into the StopFilter constructor.
     * This permits this table construction to be cached once when
     * an Analyzer is constructed.
     *
     * @deprecated Use {@link #makeStopSet(String[])} instead.
     */
    public static final Hashtable makeStopTable(String[] stopWords) {
        return makeStopTable(stopWords, false);
    }

    /**
    * Builds a Hashtable from an array of stop words,
    * appropriate for passing into the StopFilter constructor.
    * This permits this table construction to be cached once when
    * an Analyzer is constructed.
    * @deprecated Use {@link #makeStopSet(java.lang.String[], boolean)}  instead.
    */
    public static final Hashtable makeStopTable(String[] stopWords, boolean ignoreCase) {
        Hashtable stopTable = new Hashtable(stopWords.length);
        for (int i = 0; i < stopWords.length; i++) {
            String stopWord = ignoreCase ? stopWords[i].toLowerCase() : stopWords[i];
            stopTable.put(stopWord, stopWord);
        }
        return stopTable;
    }

    /**
     * Builds a Set from an array of stop words,
     * appropriate for passing into the StopFilter constructor.
     * This permits this stopWords construction to be cached once when
     * an Analyzer is constructed.
     * 
     * @see #makeStopSet(java.lang.String[], boolean) passing false to ignoreCase
     */
    public static final Set makeStopSet(String[] stopWords) {
        return makeStopSet(stopWords, false);
    }

    /**
     * 
    * @param stopWords
     * @param ignoreCase If true, all words are lower cased first.  
     * @return a Set containing the words
     */
    public static final Set makeStopSet(String[] stopWords, boolean ignoreCase) {
        HashSet stopTable = new HashSet(stopWords.length);
        for (int i = 0; i < stopWords.length; i++)
            stopTable.add(ignoreCase ? stopWords[i].toLowerCase() : stopWords[i]);
        return stopTable;
    }

    /**
     * Returns the next input Token whose termText() is not a stop word.
     */
    public final Token next() throws IOException {
        // return the first non-stop word found
        for (Token token = input.next(); token != null; token = input.next()) {
            String termText = ignoreCase ? token.termText.toLowerCase() : token.termText;
            if (!stopWords.contains(termText))
                return token;
        }
        // reached EOS -- return null
        return null;
    }
}
